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8.3 REMOTE SET BLOCK DIAGRAM
Samsung Electronics Co., Ltd
SP-C501R
－34－
Service Manual
Explanation on the Circuit
Chapter 9.
9.1 BASE SET
9.1.1 Wireless Section
Receiving status means a string of processes to check if there is any signal received from an antenna
and to analyze the signals by switching the channels, from No.1 to No. 40, in the cycle of about
160ms. after judging if the signal is from his or her own base set.
In the receiving status, the talk switch is controlled and transmission is stopped and speakers or
microphones are not being operated in order not to cause any trouble to the others.
MICOM plays a string of these controls, and the changes of channel, which are essential to the
automatic selection of 40 channels, will be explained first.
If MICOM provides the specific channel data to IC351 (frequency synthesizer IC) via a channel data
terminal, the internal decoder enters the RX Divide corresponding to the entered channel data, into
the RX Divide or TX Divide.
RX Divider supply the output of the 1
st
local oscillator of IC351 divided by the value of RX Divider to
an input terminal of the Phase Detector (hereinafter referred to as the "PD").
Reference Counter of the frequency synthesizing section of which the dividing value is fixed to 2048
keeps dividing the oscillating frequency of output 21.25MHz of TCXO, so it supply the divided
waveform of 10.6KHz to another input terminal, and this value is constant, unless the oscillating
frequency of 21.25MHz oscillator is changed.
Therefore, the error corresponding to the phase difference between 10.6KHz frequency, output of
Reference Counter, and output frequency of RX Divider at the PD is outputted, and this phase
difference is then changed into DC Voltage in the process of passing the Loop Filter, and 1
frequency, output of VCO, is decreased or increased through the driving of the VCO by this DC
Voltage, and this 1st local frequency will be locked to the constant frequency after a certain time
elapses, through the continual feedback in the process of repeated dividing and comparison. In the
other words, when the input phase of PD completely accords, PD Output becomes "0" and output
resistance becomes the infinity, so the 1
st
local frequency is stabilized, as there is no change in the
DC Voltage of VCO.
This is the detailed synthesizing process of 1
is synthesized on the same principle.
The time taken to reach the 1
st
local frequency is about 30ms. and the time taken for the synthesis of
transmitting frequency is about 60ms.
Once MICOM transmits the data of a certain channel to the Decoder of frequency synthesizing
section, then the 1
st
Lock frequency is locked after the receiving lock time elapses, so receiving
additive demodulation is performed. If the White Noise Level of the demodulated signal in the
receiving section is higher than a certain level, 'LOW' is outputted, and if it is less than a certain level,
'HIGH' is outputted.
If the output of 30dB Detector is 'LOW', the current channel is in use and if it is 'HIGH', the channel is
construed as the one not in use. Therefore, you may check if the current channel is in use by reading
20dB value after the output of the channel data and a certain time elapses. Also, you may perceive
the condition of a channel by checking 'LOW/HIGH' depending on the channel status, 'BUSY/FREE',
in the 20dB Detector circuit. The reason why you have to check 'BUSY/FREE' in the 20dB/30dB is
that you may speed up the checking process as you know if the channel is used, and you may skip
checking when the channel is 'HIGH' which means there is no data in the channel. You may speed
up the scanning process of whole channels and the formation of the communication path between the
base and the remote sets accordingly.
For example, if the current channel is not being used, or the user does not attempt to call, in other
words, if 20/30dB is 'HIGH', the same process keeps repeating by transmitting the data of the next
channel to a frequency synthesizing section.
Samsung Electronics Co., Ltd
st
received local frequency, and transmission frequency
－35－
SP-C501R
st
local
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